The court is considering whether the Defense of Marriage Act, which bars the federal government from recognizing same-sex marriages, is constitutional. It's also weighing whether it's permissible for states, in this case, California, to refuse to recognize same-sex marriages. Multiple outcomes are possible.

The court could, as some predict, strike down the section of the law banning federal recognition of same-sex marriages but leave unsettled questions related to state recognition of such unions. If that happens, health coverage problems for same-sex couples could persist, say advocates.

"Until same-sex couples can marry coast-to-coast and be entitled to equal treatment under federal law, we're going to continue to see problems," says Tara Borelli, a staff attorney at Lambda Legal, an advocacy group.

Now, nine states and the District of Columbia recognize same-sex marriage, according to the National Conference of State Legislatures.

If a same-sex couple both lives and works in the District there may not be insurance difficulties. But what if one of them works in Virginia, where same-sex marriage isn't recognized? If a Virginia-based employer doesn't voluntarily provide benefits to same-sex spouses, the employee might not be able to insure a spouse even though they're legally married in the state where they live.

It's worth noting that a growing number of employers are stepping up to the plate. In 2012, over half of employers with 10 or more workers offered same-sex health insurance benefits, according to human resources consultant Mercer.

If the Supreme Court were to strike down the section of DOMA that prohibits federal recognition of same-sex marriages but let states decide their own marriage laws, "it adds a lot of complexity," says Catherine Stamm, a senior associate at Mercer. "Which state law will apply--where they're married, where they work, where they pay taxes, or where their insurance is based?"